Bug 1006569 - [privacy] Add checkbox at sign-up

Functionally works fine for me and all the tests pass too.
I will add the unit tests and modify helper text later today and need to discuss about the deletion of user email from database usecase.

I'm not sure if you need this. I thought that `initial` was only used when there is no pre-existing record. I could be wrong, but can you test it to see if this `if` statement is in fact needed?